<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>
<body>
  <script>
    function Person(age) {
      this.age = age;
    }  

    function Student(num) {
      this.num = num;
    }

    Student.prototype = new Person(10);

    Student.prototype.eat = function () {
      console.log('eat');
    };

    let stu = new Student();
    let per = new Person(10);
    console.log('stu:');
    console.dir(stu);
    console.log('Student:');
    console.dir(Student);
    console.log('per:');
    console.dir(per);
    console.log('Person:');
    console.dir(Person);
  </script>
</body>
</html>